FIG. 13 is a perspective view of a conventional optical reflection element. This optical reflection element has mirror portion 1, pair of oscillators 3, and frame body 4. Oscillators 3 are joined to end portions of mirror portion 1, respectively. Frame body 4 surrounds outer circumferences of oscillators 3 and mirror portion 1. A straight line connecting each of joining positions 5 between mirror portion 1 and oscillators 3, and each of joining positions 6 between frame body 4 and oscillators 3 is parallel to mirror portion central axis S131 passing a center of mirror portion 1.
Each of oscillators 3 is made of plurality of oscillating plates 3A to 3D, 3E to 3H joined so as to turn back in a meander shape. In oscillating plates 3A to 3H, drive elements each made of a lower electrode layer, a piezoelectric body layer, and an upper electrode layer are arranged, respectively. Applying a voltage to these drive elements allows oscillators 3 to be driven and mirror portion 1 to perform turning (pivoting) movement.
Mirror portion 1 can scan the reflected light on a screen when light enters mirror portion 1 and mirror portion 1 turns.
Furthermore, by providing a pair of oscillators that are perpendicular to oscillators 3 and are opposed to each other via frame body 4, mirror portion 1 can be excited vertically and horizontally by the oscillation of these four oscillators. With this constitution, an image can be projected on a wall, a screen or the like.
Each of these oscillators has further a monitor element made of a lower electrode layer, a piezoelectric body layer, and an upper electrode layer. When an electric signal detected by each of these monitor elements is inputted to an upper electrode of the drive element through a feedback circuit, in theory, the optical reflection element can be constantly driven at a resonant frequency. In the above-described self-exited driving method, a large amplitude can be maintained. The above-described optical reflection element is disclosed, for example, in Patent Literature 1.
In recent years, in the optical reflection element, efficient realization of a larger mirror amplitude angle is sought. This is to perform large screen projection, using the optical reflection element. For this, it is indispensable that the amplitude angle of the mirror is large. On the other hand, a drive frequency needs to be made higher in order to increase a resolution. However, the amplitude angle is reduced in high-frequency oscillation, which is disadvantage for the large screen projection. That is, increasing the resolution makes the large screen projection difficult.